1. Field of the Invention
The present invention relates to semiconductor fabrication equipment, and more particularly, the present invention relates to methods, circuits and systems that control the application, measurement, feedback and processing of signals associated with pulsed RF power delivery to a processing chamber or electrode.
2. Description of the Related Art
In semiconductor fabrication, integrated circuit devices are fabricated from semiconductor wafers that are placed through numerous processing operations. Many of such operations are commonly carried out in processing chambers in which layers, such as dielectric and metallization materials, are successively applied and patterned to form multi-layered structures. For example, some of these layers (e.g., SiO2) are commonly deposited in chemical vapor deposition (CVD) chambers, and then photoresist materials are spin-coated and placed through photolithography patterning. When a photoresist mask is defined over a particular surface, the semiconductor wafer is placed into a plasma etching chamber in order to remove (i.e., etch) portions of the underlying materials that are not covered by the photoresist mask.
Processing chambers may be used to etch the materials or deposit the materials onto surfaces or layers of a wafer, or to implant materials into the surfaces or layers. In some physical implementations of etch, deposition, or implantation chambers, radio frequency power (RF) is used. For example, in the processing chamber, plasma may be generated by applying the RF power to an inductive coil, and typically the RF power is applied at 13.56 MHz.
Separate from the inductive coil, the wafer is mounted in the chamber on an electrode. For process control, such as controlling the etching of, or deposition onto, or implantation into, the wafer, other (or second) RF power is separately communicated to the chamber, and in particular, is applied to the electrode on which the wafer is mounted. Specific examples of the processing chambers are those configured with such inductive coil and electrode separately from each other, in which the electrode receives such second RF power, and in which that second RF power is pulsed. Methods and systems for accurately controlling the voltage level applied by the pulsed RF power, as delivered to the chuck electrode of a chamber suffer in many respects.
What is needed then, are apparatus, circuits, and methods for measuring and determining the RF bias voltage on the wafer that are not influenced by, or a function of, the duty cycle of the pulsed RF bias signal. What is also needed then, are apparatus, circuits, and methods in which the determination of a value of the RF bias voltage on the wafer is independent of the duty cycle of the pulsed RF bias signal. What is further needed then, are apparatus, circuits, and methods in which the determination of a value of the RF bias voltage on the wafer is not based on an OFF mode of the pulsed RF bias signal.
It is in this context that embodiments arise.